The CARMA-NRO Orion Survey Kong, Shuo; Arce, Héctor G.; Feddersen, Jesse R. ...
The Astrophysical journal. Supplement series,
06/2018, Letnik:
236, Številka:
2
Journal Article
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We present the first results from a new, high-resolution 12CO(1-0), 13CO(1-0), and C18O(1-0) molecular-line survey of the Orion A cloud, hereafter referred to as the CARMA-NRO Orion Survey. CARMA ...observations have been combined with single-dish data from the Nobeyama 45 m telescope to provide extended images at about 0.01 pc resolution, with a dynamic range of approximately 1200 in spatial scale. Here we describe the practical details of the data combination in uv space, including flux scale matching, the conversion of single-dish data to visibilities, and joint deconvolution of single-dish and interferometric data. A Δ-variance analysis indicates that no artifacts are caused by combining data from the two instruments. Initial analysis of the data cubes, including moment maps, average spectra, channel maps, position-velocity diagrams, excitation temperature, column density, and line ratio maps, provides evidence of complex and interesting structures such as filaments, bipolar outflows, shells, bubbles, and photo-eroded pillars. The implications for star formation processes are profound, and follow-up scientific studies by the CARMA-NRO Orion team are now underway. We plan to make all the data products described here generally accessible; some are already available at https://dataverse.harvard.edu/dataverse/CARMA-NRO-Orion.
The inner regions of barred galaxies contain substructures such as off-axis shocks, nuclear rings, and nuclear spirals. These substructures may affect star formation, and control the activity of a ...central black hole (BH) by determining the mass inflow rate. We investigate the formation and properties of such substructures using high-resolution, grid-based hydrodynamic simulations. The gaseous medium is assumed to be infinitesimally thin, isothermal, and non-self-gravitating. The stars and dark matter are represented by a static gravitational potential with four components: a stellar disk, a bulge, a central BH, and a bar. To investigate various galactic environments, we vary the gas sound speed, c sub(s), as well as the mass of the central BH, M sub(BH). Once the flow has reached a quasi-steady state, off-axis shocks tend to move closer to the bar major axis as c sub(s) increases. Nuclear rings shrink in size with increasing c sub(s), but are independent of M sub(BH), suggesting that the ring position is not determined by the Lindblad resonances. Rings in low-c sub(s) models are narrow since they are occupied largely by gas on x sub(2)-orbits and well decoupled from nuclear spirals, while they become broad because of large thermal perturbations in high-c sub(s) models. Nuclear spirals persist only when either c sub(s) is small or M sub(BH) is large; they would otherwise be destroyed completely by the ring material on eccentric orbits. The shape and strength of nuclear spirals depend sensitively on c sub(s) and M sub(BH) such that they are leading if both c sub(s) and M sub(BH) are small, weak trailing if c sub(s) is small and M sub(BH) is large, and strong trailing if both c sub(s) and M sub(BH) are large. While the mass inflow rate toward the nucleus is quite small in low-c sub(s) models because of the presence of a narrow nuclear ring, it becomes larger than 0.01 M yr super(-1) when c sub(s) is large, providing a potential explanation of nuclear activity in Seyfert galaxies.
We present H13CO+ (J = 1-0) and HNC (J = 1-0) maps of regions in Serpens South, Serpens Main, and NGC 1333 containing filaments. We also observe the Serpens regions using H13CN (J = 1-0). These dense ...gas tracer molecular line observations carried out with CARMA have an angular resolution of ∼7″, a spectral resolution of ∼0.16 km s−1, and a sensitivity of 50-100 mJy beam−1. Although the large-scale structure compares well with the Herschel dust continuum maps, we resolve finer structure within the filaments identified by Herschel. The H13CO+ emission distribution agrees with the existing CARMA N2H+ (J = 1-0) maps, so they trace the same morphology and kinematics of the filaments. The H13CO+ maps additionally reveal that many regions have multiple structures partially overlapping in the line of sight. In two regions, the velocity differences are as high as 1.4 km s−1. We identify eight filamentary structures having typical widths of 0.03-0.08 pc in these tracers. At least 50% of the filamentary structures have distinct velocity gradients perpendicular to their major axis, with average values in the range of 4-10 km s−1 pc−1. These findings are in support of the theoretical models of filament formation by 2D inflow in the shock layer created by colliding turbulent cells. We also find evidence of velocity gradients along the length of two filamentary structures; the gradients suggest that these filaments are inflowing toward the cloud core.
We present an analysis of the molecular gas distributions in the 29 barred and 15 unbarred spirals in the BIMA CO (J= 1-0) Survey of Nearby Galaxies (SONG). For galaxies that are bright in CO, we ...confirm the conclusion by Sakamoto et al. that barred spirals have higher molecular gas concentrations in the central kiloparsec. The SONG sample also includes 27 galaxies below the CO brightness limit used by Sakamoto et al. Even in these less CO-bright galaxies we show that high central gas concentrations are more common in barred galaxies, consistent with radial inflow driven by the bar. However, there is a significant population of early-type (Sa-Sbc) barred spirals (6 of 19) that have no molecular gas detected in the nuclear region and have very little out to the bar corotation radius. This suggests that in barred galaxies with gas-deficient nuclear regions, the bar has already driven most of the gas within the bar corotation radius to the nuclear region, where it has been consumed by star formation. The median mass of nuclear molecular gas is over 4 times higher in early-type bars than in late-type (Sc-Sdm) bars. Since previous work has shown that the gas consumption rate is an order of magnitude higher in early-type bars, this implies that the early types have significantly higher bar-driven inflows. The lower accretion rates in late-type bars can probably be attributed to the known differences in bar structure between early and late types. Despite the evidence for bar-driven inflows in both early and late Hubble-type spirals, the data indicate that it is highly unlikely for a late-type galaxy to evolve into an early type via bar-induced gas inflow. Nonetheless, secular evolutionary processes are undoubtedly present, and pseudobulges are inevitable; evidence for pseudobulges is likely to be clearest in early-type galaxies because of their high gas inflow rates and higher star formation activity.
We examined software usage in a sample set of astrophysics research articles published in 2015 and searched for the source codes for the software mentioned in these research papers. We categorized ...the software to indicate whether the source code is available for download and whether there are restrictions to accessing it, and if the source code is not available, whether some other form of the software, such as a binary, is. We also extracted hyperlinks from one journal's 2015 research articles, as links in articles can serve as an acknowledgment of software use and lead to the data used in the research, and tested them to determine which of these URLs are still accessible. For our sample of 715 software instances in the 166 articles we examined, we were able to categorize 418 records as according to whether source code was available and found that 285 unique codes were used, 58% of which offered the source code for download. Of the 2558 hyperlinks extracted from 1669 research articles, at best, 90% of them were available over our testing period.
We present a comparative study of molecular and ionized gas kinematics in nearby galaxies. These results are based on observations from the EDGE survey, which measured spatially resolved 12CO(J = ...1-0) in 126 nearby galaxies. Every galaxy in EDGE has corresponding resolved ionized gas measurements from CALIFA. Using a sub-sample of 17 rotation-dominated, star-forming galaxies where precise molecular gas rotation curves could be extracted, we derive CO and H rotation curves using the same geometric parameters out to 1 Re. We find that ∼75% of our sample galaxies have smaller ionized gas rotation velocities than the molecular gas in the outer part of the rotation curve. In no case is the molecular gas rotation velocity measurably lower than that of the ionized gas. We suggest that the lower ionized gas rotation velocity can be attributed to a significant contribution from extraplanar diffuse ionized gas in a thick, turbulence-supported disk. Using observations of the Hγ transition, also available from CALIFA, we measure ionized gas velocity dispersions and find that these galaxies have sufficiently large velocity dispersions to support a thick ionized gas disk. Kinematic simulations show that a thick disk with a vertical rotation velocity gradient can reproduce the observed differences between the CO and H rotation velocities. Observed line ratios tracing diffuse ionized gas are elevated compared to typical values in the midplane of the Milky Way. In galaxies affected by this phenomenon, dynamical masses measured using ionized gas rotation curves will be systematically underestimated.
We use NH3 inversion transitions to trace the dense gas in the NGC 1333 region of the Perseus molecular cloud. NH3 (1, 1) and NH3 (2, 2) maps covering an area of 102 square arcminutes at an angular ...resolution of ∼3 7 are produced by combining Very Large Array interferometric observations with Green Bank Telescope single-dish maps. The combined maps have a spectral resolution of 0.14 km s−1 and a sensitivity of 4 mJy/beam. We produce integrated intensity maps, peak intensity maps, and dispersion maps of NH3 (1, 1) and NH3 (2, 2) and a line-of-sight velocity map of NH3 (1, 1). These are used to derive the optical depth for the NH3 (1, 1) main component, the excitation temperature of NH3 (1, 1), and the rotational temperature, kinetic temperature, and column density of NH3 over the mapped area. We compare these observations with the CARMA J = 1-0 observations of N2H+ and H13CO+ and conclude that they all trace the same material in these dense star-forming regions. From the NH3 (1, 1) velocity map, we find that a velocity gradient ridge extends in an arc across the entire southern part of NGC 1333. We propose that a large-scale turbulent cell is colliding with the cloud, which could result in the formation of a layer of compressed gas. This region along the velocity gradient ridge is dotted with Class 0/I young stellar objects, which could have formed from local overdensities in the compressed gas leading to gravitational instabilities. The NH3 (1, 1) velocity dispersion map also has relatively high values along this region, thereby substantiating the shock layer argument.
Abstract
The center of the nearby galaxy NGC 253 hosts a population of more than a dozen super star clusters (SSCs) that are still in the process of forming. The majority of the star formation of the ...burst is concentrated in these SSCs, and the starburst is powering a multiphase outflow from the galaxy. In this work, we measure the 350 GHz dust continuum emission toward the center of NGC 253 at 47 mas (0.8 pc) resolution using data from the Atacama Large Millimeter/submillimeter Array. We report the detection of 350 GHz (dust) continuum emission in the outflow for the first time, associated with the prominent South-West streamer. In this feature, the dust emission has a width of ≈8 pc, is located at the outer edge of the CO emission, and corresponds to a molecular gas mass of ∼(8–17)×10
6
M
⊙
. In the starburst nucleus, we measure the resolved radial profiles, sizes, and molecular gas masses of the SSCs. Compared to previous work at the somewhat lower spatial resolution, the SSCs here break apart into smaller substructures with radii 0.4–0.7 pc. In projection, the SSCs, dust, and dense molecular gas appear to be arranged as a thin, almost linear, structure roughly 155 pc in length. The morphology and kinematics of this structure can be well explained as gas following
x
2
orbits at the center of a barred potential. We constrain the morpho-kinematic arrangement of the SSCs themselves, finding that an elliptical, angular-momentum-conserving ring is a good description of both the morphology and kinematics of the SSCs.
Kinematics of Spiral-Arm Streaming in M51 Shetty, Rahul; Vogel, Stuart N; Ostriker, Eve C ...
Astrophysical journal/The Astrophysical journal,
08/2007, Letnik:
665, Številka:
2
Journal Article
Recenzirano
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We use CO and H alpha velocity fields to study the gas kinematics in the spiral arms and interarms of M51 (NGC 5194), and fit the 2D velocity field to estimate the radial and tangential velocity ...components as a function of spiral phase (arm distance). We find large radial and tangential streaming velocities, which are qualitatively consistent with the predictions of density wave theory and support the existence of shocks. The streaming motions are complex, varying significantly across the galaxy as well as along and between arms. Aberrations in the velocity field indicate that the disk is not coplanar, perhaps as far in as 20" (800 pc) from the center. Velocity profile fits from CO and H alpha are typically similar, suggesting that most of the H alpha emission originates from regions of recent star formation. We also explore vortensity and mass conservation conditions. Vortensity conservation, which does not require a steady state, is empirically verified. The velocity and density profiles show large and varying mass fluxes, which are inconsistent with a steady flow for a single dominant global spiral mode. We thus conclude that the spiral arms cannot be in a quasi-steady state in any rotating frame, and/or that out-of-plane motions may be significant.
Abstract We present a 12 CO( J = 2−1) survey of 60 local galaxies using data from the Atacama Compact Array as part of the Extragalactic Database for Galaxy Evolution: the ACA EDGE survey. These ...galaxies all have integral field spectroscopy from the CALIFA survey. Compared to other local galaxy surveys, ACA EDGE is designed to mitigate selection effects based on CO brightness and morphological type. Of the 60 galaxies in ACA EDGE, 36 are on the star formation main sequence, 13 are on the red sequence, and 11 lie in the “green valley” transition between these sequences. We test how star formation quenching processes affect the star formation rate (SFR) per unit molecular gas mass, SFE mol = SFR/ M mol , and related quantities in galaxies with stellar masses 10 ≤ log M ⋆ / M ⊙ ≤ 11.5 covering the full range of morphological types. We observe a systematic decrease of the molecular-to-stellar mass fraction ( R ⋆ mol ) with a decreasing level of star formation activity, with green valley galaxies also having lower SFE mol than galaxies on the main sequence. On average, we find that the spatially resolved SFE mol within the bulge region of green valley galaxies is lower than in the bulges of main-sequence galaxies if we adopt a constant CO-to-H 2 conversion factor, α CO . While efficiencies in main-sequence galaxies remain almost constant with galactocentric radius, in green valley galaxies, we note a systematic increase of SFE mol , R ⋆ mol , and specific SFR with increasing radius. As shown in previous studies, our results suggest that although gas depletion (or removal) seems to be the most important driver of the star formation quenching in galaxies transiting through the green valley, a reduction in star formation efficiency is also required during this stage.
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